1. Field of the Disclosure
The present subject matter is generally directed to mobile drilling rig assemblies, and, in particular, to the use of a collapsible drilling rig substructure to facilitate both highway transportation and drilling site movement of a mobile drilling rig.
2. Description of the Related Art
In many land-based oil and gas drilling operations, drilling rigs are delivered to an oilfield drilling site by transporting the various components of the drilling rig over roads and/or highways. Typically, the various drilling rig components are transported to the drilling site on one or more truck/trailer combinations, the number of which may depend on the size, weight and complexity of the rig. Once at the drilling site, the components are then assembled, and the drilling rig mast is erected to an appropriate operating position. In many applications, the drilling rig mast is raised to a substantially vertical operating position so that drilling operations can be performed so as to drill a wellbore into the earth. For some oil and gas wells, it may be necessary to perform directional drilling operations, such that the drilled wellbore deviates from a substantially vertical orientation to an orientation that is angled to a certain degree from vertical, which in certain applications may even be angled to a substantially horizontal orientation.
In some applications, the target depth of a horizontal leg of a directionally drilled wellbore may be relatively shallow, such as in the range of 300-500 feet, whereas, in other applications, the depth of the horizontal leg may be up to 1500 feet or even deeper. In the case of such near-surface target depths, it may be necessary to initiate the drilling activities at the surface in a non-vertical orientation, i.e., at a non-zero angle relative to horizontal, so that the wellbore can be turned to a substantially horizontal orientation by the time the shallow target depth has been reached. In such cases, specially designed slant rigs may be used, where the drilling rig mast can be adjusted to a specific angle, e.g., at 45° to horizontal, during the drilling operations. Slant rigs can, therefore, provide a marked improvement in near-surface horizontal drilling applications over more traditional land-based oil and gas rigs—i.e., those with a drilling rig mast that is erected to a substantially vertical orientation. However, the relative positioning of the various slant rig components during drilling operations can lead to certain problems and/or inefficiencies during highway and/or road transportation of the slant rig components between oilfield sites, assembly and erection of the slant rig and movement of the assembled slant rig between adjacent wellbores during pad drilling.
FIGS. 1A-1E illustrate one representative prior art mobile drilling rig that has been used for slant rig drilling applications. More specifically, FIG. 1A shows a drilling rig mast assembly structure 120 positioned on a trailer 101, which is pulled by a truck 100 over a highway and/or road surface 105. The trailer 101 is supported by a plurality of wheels 102, the quantity of which may vary depending on the size and/or weight of the mast assembly structure 120. The mast assembly structure 120 includes a drilling mast 110 with a crown block assembly 111 located at an upper end thereof to facilitate movement of a top drive assembly 125 during drilling operations. The mast assembly structure 120 also typically includes one or more hydraulic cylinders 124 that are used for erecting the drilling mast 110 to a desired operating position, e.g., at a 45° angle relative to horizontal, by pivoting the mast 110 about a pinned connection 115. Furthermore, as shown in FIG. 1A, a stiff leg 121 (see, FIG. 1E) is transported in two sections—a lower section 121a that is pivotably connected to the trailer 101, and an upper section 121b that will be connected at its lower end to the lower section 121a and at its upper end to the drilling rig mast 110 after erection so as to support the mast 110 at an appropriate angle. Additionally, the mast assembly structure 120 includes connections 122a, 122b to which a rig substructure 160 (see, FIGS. 1B-1E) will be connected during assembly of the slant rig 195 (see, FIGS. 1D and 1E).
FIGS. 1B and 1C show the rig substructure 160 positioned on a trailer 151, which is pulled by a truck 150 over the highway and/or road surface 105. The trailer 151 is supported by a plurality of wheels 152, the quantity of which varies depending on the size and/or weight of the rig substructure 160. The rig substructure 160 includes a plurality of structural members 165 and bearing pad support beams 161 for supporting the dead and operating loads of the slant rig 195 (see, FIGS. 1D and 1E). Additionally, the rig substructure 160 includes connections 162a, 162b which can be connected to connections 122a, 122b of the mast assembly structure 120 (see, FIG. 1A) during rig assembly. As shown in FIG. 1B, the rig substructure 160 supports a drawworks 170, and, during transportation, also may support the wellhead equipment 190, e.g., a Christmas tree, blowout preventer (BOP), etc., as shown in FIG. 1C.
FIG. 1D shows the slant rig 195 after the rig substructure 160 has been positioned on drilling mats 180, which are placed on the surface 181 of the well site to support the slant rig 195 and other auxiliary drilling equipment (not shown) during drilling operations. Furthermore, the mast assembly structure 120 has been raised so that the connections 162a and 162b can be fastened to the connections 122a and 122b, respectively, on the mast assembly structure 120. Additionally, the drilling rig mast assembly structure 120, including the trailer 101, is supported by a plurality of jacks 130 and/or similar structural supports, the quantity and position of which may depend on the size and weight of the mast assembly structure 120.
FIG. 1E shows the slant rig 195 after the mast 110 has been erected to an appropriate angle for near-surface direction drilling, e.g., at an angle of 45° relative to horizontal. Additionally, the upper and lower sections 121b, 121a of the stiff legs 121 have been assembled so as to support the mast 110, and a drilling line 171 has been sheaved from the drawworks 170 and over the crown block 111 to support the top drive 125 during drilling operations. Furthermore, the wellhead equipment 190 is now positioned in the cellar 191, i.e., the area within the substructure 160 and below the drill floor 163.
In the rig configuration illustrated in FIG. 1E, the drawworks 170 is in a “low” position, such that it is located below the drill floor 163. However, it should be appreciated that the wellhead equipment 190 is effectively contained within a substantially “closed” cellar 191—i.e., one that is enclosed on all four sides: by the mast assembly structure 120 and trailer 101 on the front side, by the structural members 165 of the rig substructure 160 on both the driller's side and the off-driller's side, and by the drawworks 170 on the back side. As such, access to the wellhead equipment 190 for repair and/or maintenance activities during the drilling operations is restricted due to the substantially “closed” cellar 191. Additionally, it should be appreciated that the slant rig 195 cannot be moved from the current wellbore location without first disassembling the respective connections 122a, 122b and 162a, 162b, and then moving the mast assembly structure 120 and the rig substructure 160 away from wellhead equipment 190 in opposite directions. Accordingly, the slant rig 195 shown in FIG. 1E is not easily adapted for use in pad drilling operations, i.e., where multiple adjacent and/or closely-spaced wellbores are drilled at the same site location, as moving the slant rig 195 requires that the rig 195 be disassembled, the components moved on separate trailers, and then reassembled at a new wellbore location.
FIGS. 2A-2D illustrate yet another representative prior art mobile drilling rig that has been used for slant rig drilling applications. As shown in FIG. 2A, a drilling rig mast assembly structure 220 is positioned on a trailer 201 that is supported by a plurality of wheels 202, and which is pulled by a truck 200 over a highway and/or road surface 205. The mast assembly structure 220 includes a drilling mast 210 with a crown block assembly 211 located at an upper end thereof to facilitate movement of a top drive assembly (not shown) during drilling operations. The mast assembly structure 220 also typically includes a pair of hydraulic cylinders 224 that are used for erecting the drilling mast 210 to a desired operating position, e.g., at a 45° angle relative to horizontal, by pivoting the mast 210 about a pinned connection 215. Furthermore, the mast assembly structure 220 also includes a stiff leg 221 that is pivotably connected to the trailer 201 for supporting the drilling rig mast 210 after erection to an appropriate angle.
The mast assembly structure 220 also includes a rig substructure 260 having a drill floor 263, as well as a plurality of structural members 265 and bearing pad support beams 261 for supporting the dead and operating loads of the fully assembled slant rig 295 (see, FIG. 2D) during drilling operations. Additionally, the rig substructure 260 has connections 222a, 222b to which a drawworks box 270b (see, FIGS. 2B-2D) can be connected during assembly of the slant rig 295. As shown in FIG. 2A, a cellar area 291a of the substructure 260 is located below the drill floor 263.
FIG. 2B shows a truck 250 that is used to pull a trailer 251 over the highway and/or road 205. The trailer 251 supports a drawworks 270 mounted on a drawworks skid 270a, and the drawworks box 270b. The drawworks box 270b includes a plurality of structural members 275 and a floor 263b, as well as connections 262a and 262b for fastening the drawworks box 270b to connections 222a and 222b, respectively, on the rig substructure 260 (see, FIG. 2A). A cellar area 291b is located below the floor 263b of the drawworks box 270b, which is enclosed on two sides by the structural members 275. FIG. 2C is an end view of the drawworks box 270b, and shows that the cellar area 291b is substantially open between the structural members 275.
FIG. 2D shows the slant rig 295 after the connections 262a and 262b on the drawworks box 270b have been fastened to the connections 222a and 222b, respectively, on the rig substructure 260, and after the drawworks skid 270a with the drawworks 270 thereon have been positioned on the floor 263b of the drawworks box 270b. Unlike the slant rig 195 illustrated in FIG. 1E and described above, the drawworks 270 of the slant rig 295 is in a “high” position, i.e., substantially at the level of the drill floor 263a. In this assembled configuration, the cellar 291 of the slant rig 295 (which is now made up of the cellar area 291a of the rig substructure 260 and the cellar area 291b of the drawworks box 270b) is enclosed on three sides: by the rig assembly 220 and the trailer 201 on the front side, and by the structural members 265 and 275 on the driller's side and off-driller's side. The cellar 291 is open, however, from the back side of the slant rig 295. The slant rig 295 can, therefore, be moved away from a first wellbore location after drilling operations have been completed by using the truck 200 to move the trailer 201 over the surface 281 of the drilling site and away from the first wellbore location, and thereafter positioned at a second nearby wellbore location. As such, the slant rig 295 shown in FIG. 2D is more readily adaptable for pad drilling operations than the slant rig 195 illustrated in FIGS. 1A-1E.
However, it should be appreciated that, due to the fixed structure of the drawworks box 270b, the height at which the drawworks box 270b must be attached to the rig substructure 260, and the relatively high weight of the drawworks 270 (which may be as much as 30,000 pounds or even greater), the drawworks box 270b and the drawworks 270 must be assembled to the mast assembly structure 220 by using a suitably sized crane (not shown). Furthermore, due to typical height and/or weight restrictions on permits for highway and/or road transportation of heavy equipment, the drawworks box 270b and drawworks 270 usually cannot be transported by the truck 200 and trailer 201 over highways and/or roads in the fully assembled configuration shown in FIG. 2D. As such, a crane must also be used to disassemble the slant rig 295 after the drilling operations at a given pad drilling site have been completed. Accordingly, logistical considerations for using the slant rig 295 in pad drilling operations must include having a crane present at a given pad drilling site prior to the commencement of drilling operations in order to facilitate initial rig assembly. Furthermore, a crane must also be present after the completion of pad drilling operations so as to facilitate rig disassembly for transportation to other pad drilling sites. As may be appreciated, the requirement that a crane be used during these stages can have a significant impact on the overall cost of the drilling operation, as well as the amount of time that may be needed to perform the operations.
Accordingly, there is a need to develop and implement new designs and methods for facilitating the transportation of a mobile drilling rig, such as a slant drilling rig and the like, between various drilling sites without relying on the use of a crane to assemble and disassemble the rig, as well as enabling the mobile drilling rig to be moved between adjacent wellbore locations during pad drilling operations without first disassembling the rig.